understanding stateful vs stateless communication strategies for ad hoc networks victoria manfredi,...

Understanding Stateful vs Stateless Communication

Strategies for Ad hoc Networks

Understanding Stateful vs Stateless Communication

Strategies for Ad hoc Networks

Victoria Manfredi, Mark Crovella, Jim Kurose

MobiCom 2011

2

Static: stateful strategies work well

High mobility: stateful strategies can work poorly

Topology instability

Problem

Many communication strategies: routing, flooding, DTN

But when is each appropriate?

3

Static: stateful strategies work well

High mobility: stateful strategies can work poorly

Topology instability

Problem

But when is each appropriate?

When precisely do stateful vs stateless communication strategies

maximize goodput?

Many communication strategies: routing, flooding, DTN

4

1. Problem identify when stateful vs stateless strategies max goodput

2. Proposed framework introduce instantiate evaluate

3. Related work

4. Open questions

5. Summary

Outline

network modelsdata traces

5

1. Problem identify when stateful vs stateless strategies max goodput

2. Proposed framework introduce instantiate evaluate

3. Related work

4. Open questions

5. Summary

Outline

network modelsdata traces

6

Control state info about network e.g., what links/paths

exist?

Proposed Framework

Valuable when network is predictable

What state should communication strategies maintain?

7

Control state info about network e.g., what links/paths

exist?

Proposed Framework

As contention (e.g., # of flows) increases, control state may

be valuable even in an unpredictable network (cost of control state is amortized)

What state should communication strategies maintain?

8

Proposed Framework

Data state info about data pkts e.g., how long to buffer

data pkts?

Valuable when network is not well-connected

What state should communication strategies maintain?

9

Proposed Framework

Putting it all together 4 classes of strategies

What state should communication strategies maintain?

10

Proposed Framework

Putting it all together 4 classes of strategies

What state should communication strategies maintain?

Routing Flooding

Hybrid DTN

11

Proposed Framework

Putting it all together 4 classes of strategies but, how to instantiate

framework?

What state should communication strategies maintain?

Need empirical measures to quantify unpredictability, contention, connectivity

Routing Flooding

Hybrid DTN

12

Unpredictability average link-up

entropy, h

Contention number of flows in

network, N

Connectivity probability arbitrary

route exists,

Instantiating the Framework

0 1 h

Link-up entropy, H(gt+i | gt) gt: arbitrary link up/down in Gt

Average link-up entropy, h

Network at time t Network at time t+iState of links that

were up when control state last collected:

link-up state

Gt Gt+i

(control state collected)

Average Link-up Entropy, h

…

1 H(gt+1|gt) H(gt+2|gt) + …

T

t

h = + +

Link-up entropy, H(gt+i | gt) gt: arbitrary link up/down in Gt

Average link-up entropy, h

Network at time t Network at time t+iState of links that

were up when control state last collected:

link-up state

Gt Gt+i

(control state collected)

Average Link-up Entropy, h

…

1 H(gt+1|gt) H(gt+2|gt) + …

T

t

# of timesteps

15

0 1

Unpredictability average link-up

entropy, h

Contention number of flows in

network, N

Connectivity probability arbitrary

route exists,

Instantiating the Framework

h=0.5 f(N)

S1

D1

Routing FloodingS1

D1

16

0 1

Unpredictability average link-up

entropy, h

Contention number of flows in

network, N

Connectivity probability arbitrary

route exists,

Instantiating the Framework

h=0.5 f(N)

S1

D1

Routing FloodingS1

D1

1/2

S2

D2

1/2

S2

D2

1 1

17

0 1

Instantiating the Framework

h=0.5 f(N)

=0.5

1

0

Unpredictability average link-up

entropy, h

Contention number of flows in

network, N

Connectivity probability arbitrary

path exists,

End-to-end path likely

to exist

End-to-end path unlikely

to exist

18

0 1

Instantiating the Framework

h=0.5 f(N)

=0.5

1

0

Unpredictability average link-up

entropy, h

Contention number of flows in

network, N

Connectivity probability arbitrary

path exists,

19

0 1

Instantiating the Framework

h=0.5 f(N)

=0.5

1

0

Unpredictability average link-up

entropy, h

Contention number of flows in

network, N

Connectivity probability arbitrary

path exists,

How well does framework identify when stateful vs stateless strategy

is appropriate?

20

1. Problem identify when stateful vs stateless strategies max goodput

2. Proposed framework introduce instantiate evaluate

3. Related work

4. Open questions

5. Summary

Outline

network modelsdata traces

21

0 1 h=0.5 f(N)

=0.5

How well does framework identify when stateful vs stateless strategy is appropriate?

Evaluating the Framework

Network models to evaluate entire

parameter space (h, N, )

Data traces to check framework

is useful for real networks

22

Packet TransmissionPacket received by all nodes reachable at timestep

Link capacity of 1, can use for control or data pkt

up

p

1-q

q1-p

Network Model Simulations

Random Waypoint 100 nodes 1000m x 1000m area constant velocity, no pause perfect simulation

down

…

Control Data

?

Communication StrategiesRouting: transmit pkt over shortest path

Flooding: flood pkt to all nodes reachable at current timestep

(Simplified) DTN: flood pkt to all nodes reachable within 2 timesteps

Torus Link model

Torus

No way to map where a strategy does well in one network model to another network model

Lack of DTN for RWP is due to simplified DTN strategy

Route Flood DTN None

RWP

Results in Original Parameter Space (2 Flows)

23

24

Results in Framework Space (2 Flows)

Torus RWP

h

h h Route Flood DTN None

Regions where different strategies maximize goodput are similar

25

Results in Framework Space (7 Flows)

Increasing network contention increases the probability that a control state strategy (routing) is appropriate

Framework consistently organizes decision space

Torus RWP

h

h h

Route Flood DTN None

26

HaggleInfocom06: 78 participants, 20 access points Infocom05: 41 participantsIntel: 8 employees Cambridge: 12 grad students

DieselNet21 busesAdd 2 hours after end of bus schedules for day

• assume buses in garage• adjacent buses communicate

Discrete-time simulation1 timestep = 1 s Plot exponentially weighted moving average of measures (weight of 0.001)

Expect to be in datastate (DTN) region

Expect to finish in control state (routing) region

Data Trace Simulations

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Analysis of Data TracesWhat type of state should be maintained?

Surprisingly: control+data state strategies appropriate

Tim

e-A

vera

ged

Time-Averaged h h

DieselNet

Infocom05

Intel

Infocom06

Cambridge

28

Compare hybrid forwarding with routing and (more realistic) DTN forwarding

Pkt generation: flows between all node pairs, select random flow at each timestep and add pkt to queue

Control+Data State Region

Low connectivity+low unpredictability few paths but paths are stable

Simple control+data state strategy if path exists to destination, use routing else use DTN forwarding via neighbors

Hybrid forwarding

29

Infocom06 Trace

…

…

30

Infocom06 Trace

…

…

Control+Data

31

Infocom06 Trace

…

…

Control+DataRouting : 152,491 packets deliveredDTN forwarding : 159,682Hybrid forwarding : 168,059

…

32

Infocom06 Trace

…

…

Control+DataRouting : 152,491 packets deliveredDTN forwarding : 159,682Hybrid forwarding : 168,059

As predicted by framework, hybrid forwarding is most appropriate strategy

for control+data state region

…

33

DieselNet Trace

…

…

34

DieselNet Trace

…

…

t=1 t=56701 t=63860

Data Control

35

DieselNet Trace

…

…

…

t=1 t=56701 t=63860

Data R: 23692D: 8332 H: 23268

Routing : 827 packets delivered DTN forwarding : 1531Hybrid forwarding : 1179

Control

36

DieselNet Trace

…

…

…

t=1 t=56701 t=63860

Data R: 23692D: 8332 H: 23268

Routing : 827 packets delivered DTN forwarding : 1531Hybrid forwarding : 1179

Control

As predicted by framework, DTN forwarding is most appropriate for data state region and routing

is most appropriate for control state region

Other traces: strategies suggested by framework for the regions the traces fall into max goodput

Can always choose to switch to another region, e.g., by increasing transmission energy

For hybrid-style strategy to always be best, need to tune correctly, so that

reduces to DTN forwarding in data state region reduces to routing in control state region

37

network modelsdata traces

1. Problem identify when stateful vs stateless strategies max goodput

2. Proposed framework introduce instantiate evaluate

3. Related work

4. Open questions

5. Summary

Outline

38

Organizing the space of strategies Ramanathan, Basu, Krisnan, 2007

• classify network based on level of connectivity, formalize routing mechanism needed for each class

Chen, Borrel, Ammar, Zegura, 2011• classify node pairs based on connectivity of path between nodes and path

persistence, classify network based on proportion of nodes of each type

Our focus: when to maintain state, what state to maintain

Hybrid-style strategies Ott, Kutscher, Dwertmann, 2006

• modify AODV to use DTN-capable nodes if no route to destination Chen, Zhao, Ammar, Zegura, 2007

• clustered DTNs: route within clusters, message ferry between clusters Whitbeck, Conan, 2010

• form groups then distance vector within group, DTN between groups

Our focus: simple strategy to compare with routing, DTN

Related Work

39

Organizing the space of strategies Ramanathan, Basu, Krisnan, 2007

• classify network based on level of connectivity, formalize routing mechanism needed for each class

Chen, Borrel, Ammar, Zegura, 2011• classify node pairs based on connectivity of path between nodes and path

persistence, classify network based on proportion of nodes of each type

Our focus: when to maintain state, what state to maintain

Hybrid-style strategies Ott, Kutscher, Dwertmann, 2006

• modify AODV to use DTN-capable nodes if no route to destination Chen, Zhao, Ammar, Zegura, 2007

• clustered DTNs: route within clusters, message ferry between clusters Whitbeck, Conan, 2010

• form groups then distance vector within group, DTN between groups

Our focus: simple strategy to compare with routing, DTN

Related Work

40

Open Questions

Distributed algorithms to estimate measures– gossip algorithms– estimate local measures for different network regions

Adaptive forwarding strategies– algorithm that maintains both control state and data state

• vary amount of state maintained both spatially and temporally• reduces to routing, flooding, DTN forwarding when appropriate

Better measures of connectivity, unpredictability, and contention?– interference, energy, social ties, known (bus) schedules

41

Summary

Instantiated– (h,,N): measures that could

be estimated in deployed network

Evaluated– correctly and consistently

organized decision space– identified need for new class

of communication strategies

Framework for understanding when/what state communication strategy should maintain

Thank you! Questions?

42

Back-up slides

43

Torus: Average Goodput for One Sender

Routing

q p p

DTN, =2

Routing goodput increases as links stay up longer or link changes become more predictable

Percolation: threshold for high/low flooding goodput

Flooding

qq p

Percolation threshold

Percolation threshold

DTN goodput decays more slowly than flooding below percolation threshold

44

Flooding has greatest gains relative to routing when link state highly uncertain (p≈q): high avg link-up entropy and at percolation threshold

Flooding / Routing

Torus: Goodput Relative to Flooding

q p q p

Avg Link-Up Entropy

Percolation threshold

45

Torus: Goodput Relative to Flooding

Flooding has greatest gains relative to routing when link state highly uncertain (p≈q): high avg link-up entropy and at percolation threshold

Flooding / Routing

q

Flooding has smallest gains relative to DTN when end-to-end paths unlikely to exist: below percolation threshold

q p

Flooding / DTN, =2

Percolation threshold

p

46

Torus: Average Link Entropy

p=q=0.99

p=q=0.5

p=q=0.9

p=q=0.01p=q=0.99

p=q=0.01

p=q=0.9

p=q=0.5

47

Torus: Average Link(-Up) EntropySimulation

Avg Link-Up EntropyTheoretical

Avg Link-Up EntropyTheoretical

T*

q p q p

qp

0 0

1

0 00 0

11

1 1

1

48

RWP: Average Goodput for One Sender

RoutingDTN, =2

Velocity(m/s)

Radius (m) Velocity

m/s Radius(m)

Flooding

Velocity (m/s) Radius(m)

Percolation threshold

Routing goodput increases as links stay up longer or link changes become more predictable

Percolation: threshold for high/low flooding goodput

DTN goodput decays more slowly than flooding below percolation threshold

Percolation threshold

49

Flooding has greatest gains relative to routing when link state highly uncertain (high velocity, smallish radius): high avg link-up entropy and at

percolation threshold

RWP: Goodput Relative to Flooding

Velocity (m/s)

Radius (m)

Avg Link-Up Entropy

Percolation threshold

Flooding / Routing

Velocity (m/s)

Radius (m)

50

RWP: Goodput Relative to Flooding

Flooding has smallest gains relative to DTN when end-to-end paths unlikely to exist: below percolation threshold

Velocity (m/s)

Radius (m)

Flooding / DTN, =2

Percolation threshold

Flooding / Routing

Velocity (m/s)

Radius (m)

Flooding has greatest gains relative to routing when link state highly uncertain (high velocity, smallish radius): high avg link-up entropy and at

percolation threshold

51

RWP: Average Link-Up Entropy

Up Links Only Up Links and Down Links